Currently, it is common to form various systems on semiconductor chips. General purpose processors, digital signal processors, Application Specific Integrated Circuits (ASICs), and the like are manufactured by forming a variety of transistors, resistors, capacitors, inductors, etc., on a semiconductor substrate.
The processes that are used to form the circuit elements on a semiconductor substrate are sometimes less than ideal and cause some amount of process variation in the circuit elements. Process variation, in general, is the difference between an actual quality of a circuit element and its nominal quality. For instance, capacitors formed in semiconductor chips tend to have process variation of up to approximately plus or minus 20%, depending on the process. Thus, the actual capacitance of a given capacitor on a chip, measured in Farads, may be significantly different from the intended or nominal value specified in the design.
One application that uses capacitors is a tuner circuit. Specifically, such tuner circuits may include input filtering functions to condition input signals before they are passed to other tuner components. Most such filters are Inductive-Capacitive (LC) circuits. The frequency response of a given LC filter depends on the values of the capacitor(s) and inductor(s) in the circuit. Thus, capacitor variation can cause frequency response shifts in filters, causing non-ideal operation.
Prior art solutions have compensated for capacitor variation by measuring time-constant change in one or more Resistive-Capacitive (RC) circuits. However, since the time constant in an RC circuit is equal to resistance times capacitance, and since resisters also usually include a non-negligible amount of variation, time constant deviation fails to allow for the isolation of capacitor process variation. Thus, capacitor variation can only be approximated or guessed from the time constant deviation. The prior art offers no system that can accurately measure capacitor variation for a group of capacitors in an application.